Heat Transfer Modeling of the Capillary Fiber Drawing Process

Abstract

Considerable recent research has focused on the ability of microstructured fibers to exhibit diverse optical functionalities. However, accurately preserving the structure imposed at the preform stage after drawing it down to fiber, while avoiding Rayleigh–Plateau style instabilities, has proven to be a major fabrication challenge. This modeling/analytical study was carried out in support of an experimental program into possible fabrication options for various microstructured optical fibers and considers the generic case of the nonisothermal drawing of a capillary preform to fiber. Model development was carried out in two stages. Initially, a fully conjugate multiphase model, which includes all heat transfer modes within an operational fiber drawing furnace, was validated against available experimental data. To evaluate the external radiative heat flux using the net-radiation method, a Monte Carlo ray-tracing (MC-RT) method was coupled to the commercial polyflow package to obtain all view factors between the various furnace walls and the deforming preform/fiber. A simplified model was also developed (to shorten simulation run times) by explicitly calculating the convective heat transfer between the air within the furnace and the preform/fiber surface using a heat transfer coefficient determined by matching predicted results with those obtained from the multiphase model.